High frequency apparatus



June 24, 1941. RAMQ 2,247,338

HIGH FREQUENCY APPARATUS Filed Nov. 30, 1939 Inventor: Simon Ramo,

His Attorney.

Patented June 24, 1941 HIGH FEEQUENCY APTARATUS Simon Raine, Schenectady, N. TL, assignor to General Electric Company, a corporation of New York Application November 30, 1939, Serial No. 306,952

3 Claims.

This invention relates to improvements in electronic apparatus for use at frequencies so high that electron transit time considerations play a controlling part in the operation of the apparatus.

It is a primary object of the invention to de-- crease the amount of apparatus required at a station at which it is desired to receive simul taneously two or more independent signals of dilfering frequency. In the attainment of this object, an important feature of the invention consists in the provision of means by which a single electronic device may be used for the simultaneous amplification of two or more concurrently applied signals,

The features of the invention which I desire to protect herein are pointed out in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the drawing in which the single figure represents diagrammatically an electronic apparatus suitably embodying the invention.

The apparatus shown in the drawing comprises an electron beam tube which includes an evacuated envelope having an elongated tubular portion [0. This portion, which is of uniform diameter along its length, connects at one end with an enlarged electrode containing portion l i.

The envelope is preferably constituted of a lowloss insulating material such as glass, or quartz, or the like.

The tubular envelope portion it is provided at one end with means, such as a known type of electron gum, for producing an electron beam. The combination which is shown for this purpose comprises a cathode 14 which is indicated in dotted outline and a focusing cylinder 15 for focusing the electrons emitted from the cathode into a concentrated beam. The cylinder may either by connected directly to the cathode as shown, or maintained a few volts positive or negative with respect to it. In order to accelerate the electrons to a desired extent, there is provided an accelerating electrode 16 which is spaced from the cathode and which may be biased to a suitable positive potential, say several hundred volts,

After the electron beam issues from the cylin drical electrode [6, it is caused to traverse a region of relatively fixed beam Velocity which is defined by two ring-like electrodes I3 and it. After passing through the electrode l 9, the beam is caused to impinge on an anode 28 by which it is collected.

In the operation of the apparatus the electrodes i3 and l9 are ordinarily held at a potential on the order of several thousand volts above the cathode. The anode 20 may appropriately be maintained at a somewhat lower potential for efficient collection of the beam. These potential relationships may be established by means of a suitable voltage source which is conventionally illustrated as a battery 24. In order to maintain the beam in focus during its passage along the axis of the envelope, one may employ a series of magnetic focusing coils (not shown) or other known focusing means.

The combination of elements so far described comprises means for producing a unidirectional beam of electrons. Outside the envelope there is provided a high frequency electrode system de-- signed for effective cooperation with the beam. The parts which make up the high frequency electrode system include a series of sequentially arranged tubular conductive members which concentrically surround the envelope and which are respectively numbered 26 to 34, inclusive. The tubular elements which bear even numbers are conductively connected and are held at a common potential by connection to the positive terminal of the battery 24. The members Ti, 29, 3! and 33 constitute independent electrodes which are capable of varying in potential with respect to the fixed potential parts of the system. If desired, the whole high frequency electrode system may be enclosed within a grounded conductive shield, (not shown) for the purpose of lessening radiation and of minimizing backcoupling between the various electrodes.

For the purposes of my present invention the members 2Z5, 2? and 28 may be considered as elements of an input electrode system. It has been shown by W. C. Hahn in his application Serial No. 153,602, filed July 14, 1937, that at ultra high frequencies a system of this character may be made to function very effectively as a high frequency control means provided a proper correlation exists between the axial dimensions of the conductive parts, the average velocity of the electron beam and the desired frequency of operation of the system. Specifically, if it be assumed that the member 2'! is cyclically raised and lowered in potential with respect to the members 26 and 28, maximum effect of the member on the beam occurs if the electron transit time through the member corresponds approximately to a half cycle of. the potential variation or to some odd number of such half cycles. Where this condition is fulfilled, cumulative effects occur in the two gaps which bound the member 21. Specifically, these effects will be such as to result in the presence of definite velocity diiferences in the elements of the beam which successively enter the member 28.

The velocity differences above referred to are of a cyclically repetitive pattern and correspond to so-called velocity modulation of the beam. It has been demonstrated that as a beam which is so modulated progresses along its path, the velocity variations tend to produce or to become converted into charge density variations of a higher order of magnitude. This conversion process may be utilized in the production of amplification efiects.

In the present case the conversion of velocity modulation into charge density modulation is facilitated by permitting the beam, after its issuance from the member 21, to traverse a relatively long drift space in which sorting or bunching of the fast and slow electrons can occur. At least a portion of this space is defined by the elongated member 30, which provides a relatively field free region within its confines.

Amplification effects are obtained by appropriate employment of the member 3|, which, for the purposes of the present invention, is caused to serve as an output electrode. Assuming that the axial dimensions of this electrode are properly correlated to the spacing between adjacent charge density maxima and minima in the beam, as will be the case, for example, if the dimensions of the member 3! are approximately the same as those of the member 21, currents will be induced in the member 3! as a result of the passage of the modulated beam therethrough. By connecting the electrode to a circuit of proper characteristics, output voltages of useful magnitude may be obtained.

In order that the members 2'0 and 3| may constitute parts of a complete amplification system, it is necessary, of course, that they be associated with appropriate input and output circuit ele- A ments. In the present case, an input circuit has been illustrated conventionally as comprising the parallel combination of a condenser 40 and an inductance ll, these elements being assumed to be resonant at a particular signal frequency desired to be received. For impressing such a signal on the system, the circuit 49, M is coupled to a receiving antenna :32.

In similar fashion, the output electrode 35 is connected to an output circuit which includes a condenser 54 and an inductance 45 and which is provided with output terminals 46. It is contemplated that the circuit 44, 45 shall be tuned to the same frequency as the input circuit 45], 4| or in some cases to a harmonic frequency thereof.

As has been previously pointed out, it is an object of my invention to use a single electron stream to effect amplification of several simultaneously received signals. To this end, in the apparatus illustrated the members 29 and 33 are used as parts of a second energy-conversion system which is entirely independent of the system formed by the members 21 and 34 and their associatcd circuits.

In this connection, it will be noted that the member 29 is of different length from the member 21. Consequently, for a given beam Velocity, effective reaction of the member 29 on the beam in respect to modulating the same can be obtained by impressing n the member a signal of a frequency which is different from that required for most efiective action of the member 21. It is, therefore, feasible to make the member 29 a part of an input system which is adapted to be excited by a signal quite different from that to which the circuit 68, M is tuned. An input circuit for receiving such a signal is indicated as comprising an antenna 48 and the tuned combination of an inductance 49 and a condenser 50.

At the other end of the beam path, a second output circuit, comprisin an inductance 52, a condenser 53 and output terminals 54, is provided in connection with the conductive member 33. This member is preferably of the same dimensions as the member 29 and is, therefore, selectively responsive to the charge density variations developed in the beam as a result of the modulating action of the latter electrode. For this reason, if the output circuit 52, 53 is tuned to the same frequency as the signal which is applied to the electrode 29, an amplified voltage of this frequency may be obtained at the terminals 54.

It may be demonstrated that the mechanism of signal propagation along an electron stream by a system of the type described above is such that for signals of reasonable magnitude no objectionable mixing or interference of two simultaneously propagated signals occurs. Consequently, in the apparatus which has been described in the foregoing, if the two output circuits are sharply tuned and if the two received signals are reasonably separated in frequency, simultaneous and non-interfering operation of the two amplifying systems may be realized.

An arrangement such as that which has been described above is of special value in any situation wher space or reserve equipment is limited. For example, my invention may be advantage ously employed at an emergency station where it is desired to have several channels of communication simultaneously operative and where at the same time, it is impractical to set up a large number of completely separate signal-receiving units. It will be understood, of course, that by using an electron beam tube of sufficient length, any number of independent receiving cir-- cuits may be coupled to a single beam so that duplication of the electronic component of the various receiving systems is unnecessary. It will ordinarily be possible to assemble the circuit elements of the various systems in a compact space so that the complete arrangement occupies very little more space than that required for a single receiver.

While I have described my invention by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desir to secure by Letters Patent of the United States is:

1. In apparatus for use at frequencies so high that transit time considerations play a controlling part in the operation of the apparatus, the combination which includes means for producing a stream of electrons, a pair of input systems separately coupled to the stream for producing velocity modulation of the stream at two different ultra-high frequencies, means providing a drift space of substantial length to be traversed by the stream after velocity modulation thereof, and a pair of output systems separately coupled to the beam so as to b affected by the high frequency variations existing in the stream after its issu--v ance from the said space, each of said output systems being adapted to be selectively excited at a frequency corresponding to the input frequency of one of the said input systems.

2. In ultra-high frequency apparatus utilizing a single electronic device for the simultaneous amplification of two simultaneously applied input signals of different frequency, the combination which includes an elongated tubular envelope forming a part of the said electronic device, means within said envelope for producing therein a beam of electrons of fixed average velocity, a plurality of mutually spaced conductive members sequentially coupled to the said beam and dimensionally correlated to the beam velocity, a first input and a first output system respectively connected with certain ones of said members which are positioned at appreciably spaced points along the beam axis, and a second input and a second output system respectively connected with certain others of said members which are also positioned at appreciably spaced points along the beam axis, said first and second input and output systems being respectively adapted to be selectively excited at the first and second of the said simultaneously applied signal frequencies.

3. In high frequency apparatus, the combination which includes means for producing a beam of electrons of fixed average velocity, a plurality of variously dimensioned conducting members successively coupled to said beam at spaced points thereof, a certain pair of said members constituting respectively an input and an output electrode having axial dimensions which are so correlated to the beam velocity as to assur selective reaction with the beam for a first frequency of operation of the apparatus and a certain other pair of said members constituting respectively an input and an output electrode having axial dimensions which are so correlated to th beam velocity as to assure selective reaction with the beams for a second frequency of operation of the apparatus, and two input and two output circuits respectively and independently associated with the various input and output electrodes, whereby said apparatus may be simultaneously operated at said first and second operating frequencies.

SIMON RAMO. 

